Cell biology. Insulin finds its niche

Insulin resistance disrupts epithelial repair and niche-progenitor Fgf signaling during chronic liver injury

Insulin provides important information to tissues about feeding behavior and energy status. Defective insulin signaling is associated with ageing, tissue dysfunction, and impaired wound healing. In the liver, insulin resistance leads to chronic damage and fibrosis, but it is unclear how tissue-repair mechanisms integrate insulin signals to coordinate an appropriate injury response or how they are affected by insulin resistance. In this study, we demonstrate that insulin resistance impairs local cellular crosstalk between the fibrotic stroma and bipotent adult liver progenitor cells (LPCs), whose paracrine interactions promote epithelial repair and tissue remodeling. Using insulin-resistant mice deficient for insulin receptor substrate 2 (Irs2), we highlight dramatic impairment of proregenerative fibroblast growth factor 7 (Fgf7) signaling between stromal niche cells and LPCs during chronic injury. We provide a detailed account of the role played by IRS2 in promoting Fgf7 ligand and receptor (Fgfr2-IIIb) expression by the two cell compartments, and we describe an insulin/IRS2-dependent feed-forward loop capable of sustaining hepatic re-epithelialization by driving FGFR2-IIIb expression. Finally, we shed light on the regulation of IRS2 and FGF7 within the fibrotic stroma and show—using a human coculture system—that IRS2 silencing shifts the equilibrium away from paracrine epithelial repair in favor of fibrogenesis. Hence, we offer a compelling insight into the contribution of insulin resistance to the pathogenesis of chronic liver disease and propose IRS2 as a positive regulator of communication between cell types and the transition between phases of stromal to epithelial repair.

“Insulin resistance” is a chronic state of reduced sensitivity to the effects of circulating insulin. It is one of the hallmarks of metabolic disease and a consequence of ageing, but insulin resistance is also observed in otherwise healthy individuals after severe trauma/hemorrhage/sepsis, suggesting that it plays a physiological role in modulating the response to injury. Defective insulin signals are linked to impaired wound healing, yet it remains unclear how systemic changes affect locally the cells that coordinate tissue repair. In this study, we used the liver to assess how insulin resistance impacts the injury response in mice. We provide proof of concept that insulin signals are locally integrated by the fibrotic microenvironment surrounding the adult liver stem cells during chronic injury, resulting in the increased expression of epithelial repair signals. Insulin also simultaneously primes stem cells to respond to these stromal growth factors, leading to an increased participation in epithelial repair. Insulin resistance disrupts this local paracrine circuit, resulting in a blunted epithelial response to chronic injury that exacerbates tissue damage. Our model highlights a potential role for insulin in switching the hepatic injury response from a stromal repair process to an epithelial repair process. To our knowledge, our data provide a new perspective from which to reassess how insulin resistance influences fibrosis, wound healing, and tissue remodeling during injury.

Neurotrophic and Neuroregenerative Effects of GH/IGF1

Introduction. Human neurodegenerative diseases increase progressively with age and present a high social and economic burden. Growth hormone (GH) and insulin-like growth factor-1 (IGF-1) are both growth factors exerting trophic effects on neuronal regeneration in the central nervous system (CNS) and peripheral nervous system (PNS). GH and IGF-1 stimulate protein synthesis in neurons, glia, oligodendrocytes, and Schwann cells, and favor neuronal survival, inhibiting apoptosis. This study aims to evaluate the effect of GH and IGF-1 on neurons, and their possible therapeutic clinical applications on neuron regeneration in human subjects. Methods. In the literature, we searched the clinical trials and followed up studies in humans, which have evaluated the effect of GH/IGF-1 on CNS and PNS. The following keywords have been used: “GH/IGF-1” associated with “neuroregeneration”, “amyotrophic lateral sclerosis”, “Alzheimer disease”, “Parkinson’s disease”, “brain”, and “neuron”. Results. Of the retrieved articles, we found nine articles about the effect of GH in healthy patients who suffered from traumatic brain injury (TBI), and six studies (four using IGF-1 and two GH therapy) in patients with amyotrophic lateral sclerosis (ALS). The administration of GH in patients after TBI showed a significantly positive recovery of brain and mental function. Treatment with GH and IGF-1 therapy in ALS produced contradictory results. Conclusions. Although strong findings have shown the positive effects of GH/IGF-1 administration on neuroregeneration in animal models, a very limited number of clinical studies have been conducted in humans. GH/IGF-1 therapy had different effects in patients with TBI, evidencing a high recovery of neurons and clinical outcome, while in ALS patients, the results are contradictory. More complex clinical protocols are necessary to evaluate the effect of GH/IGF-1 efficacy in neurodegenerative diseases. It seems evident that GH and IGF-1 therapy favors the optimal recovery of neurons when a consistent residual activity is still present. Furthermore, the effect of GH/IGF-1 could be mediated by, or be overlapped with that of other hormones, such as estradiol and testosterone.

The Systemic Control of Growth

Growth is a complex process that is intimately linked to the developmental program to form adults with proper size and proportions. Genetics is an important determinant of growth, as exemplified by the role of local diffusible molecules setting up organ proportions. In addition, organisms use adaptive responses allowing modulating the size of individuals according to environmental cues, for example, nutrition. Here, we describe some of the physiological principles participating in the determination of final individual size.

Control of brain development and homeostasis by local and systemic insulin signalling

Insulin and insulin-like growth factors (IGFs) are important regulators of growth and metabolism. In both vertebrates and invertebrates, insulin/IGFs are made available to various organs, including the brain, through two routes: the circulating systemic insulin/IGFs act on distant organs via endocrine signalling, whereas insulin/IGF ligands released by local tissues act in a paracrine or autocrine fashion. Although the mechanisms governing the secretion and action of systemic insulin/IGF have been the focus of extensive investigation, the significance of locally derived insulin/IGF has only more recently come to the fore. Local insulin/IGF signalling is particularly important for the development and homeostasis of the central nervous system, which is insulated from the systemic environment by the blood-brain barrier. Local insulin/IGF signalling from glial cells, the blood-brain barrier and the cerebrospinal fluid has emerged as a potent regulator of neurogenesis. This review will address the main sources of local insulin/IGF and how they affect neurogenesis during development. In addition, we describe how local insulin/IGF signalling couples neural stem cell proliferation with systemic energy state in Drosophila and in mammals.

Contributions of metabolic dysregulation and inflammation to nonalcoholic steatohepatitis, hepatic fibrosis, and cancer

PURPOSE OF REVIEW

We review accumulating evidence that nonalcoholic steatohepatitis (NASH), a more advanced form of nonalcoholic fatty liver disease (NAFLD), predisposes patients to the risk of developing hepatocellular carcinoma (HCC), and we summarize recent advances in the elucidation of cancer-promoting pathways in NASH. We highlight the potential role of progenitor cells and hepatic stellate cells (HSCs) in promoting the early events that could culminate in cancer, as well as the emerging contribution of the gut-liver axis in promoting inflammation, senescence, and tumor growth in NASH and HCC. Finally, we review the role of bile acid receptors, vitamin D, and protective cellular pathways such as autophagy.

RECENT FINDINGS

Studies have recently uncovered roles for gut microbiota, bile acid receptors and vitamin D in regulating the progression from NAFLD to HCC. Intriguing findings linking senescence and autophagy in hepatic stellate cells to HCC have also been discovered, as well as a link between dysregulated progenitor cell regulation and HCC.

SUMMARY

NAFLD is the most common cause of chronic liver disease in the United States and Western Europe. The lack of definitive mechanisms underlying development of NASH among patients with NAFLD and its progression to HCC limit diagnosis and management, but new findings are paving the way for better biomarkers and therapies.

Doxycyclin ameliorates a starvation-induced germline tumor in C. elegans daf-18/PTEN mutant background

Managing available resources is a key necessity of each organism to cope with the environment. The nematode C. elegans responds to nutritional deprivation or harsh environmental conditions with a multitude of developmental adaptations, among them a starvation-induced quiescence at early larval development (L1). daf-18, the C. elegans homolog of the human tumor suppressor gene PTEN, is essential for the maintenance of survival and germline stem cell arrest during the L1 diapause. We show here that daf-18 mutants, independently to their failure to maintain G2 arrest of the primordial germ cells, develop a gonad phenotype after refeeding. This highly penetrant gonadal phenotype is further enhanced by a mutation in shc-1, encoding a protein homologous to the human adaptor ShcA. Features of this phenotype are a tumor-like phenotype encompassing hyper-proliferation of germ cell nuclei and disruption/invasion of the basement membrane surrounding the gonad. The penetrance of this phenotype is reduced by decreasing starvation temperature. In addition, it is also ameliorated in a dose-dependent way by exposure to the antibiotic doxycyclin either during starvation or during subsequent refeeding. Since, in eukaryotic cells, doxycyclin specifically blocks mitochondrial translation, our results suggest that daf-18 and shc-1;daf-18 mutants fail to adapt mitochondrial activity to reduced nutritional availability during early larval developing.

Divergent and convergent roles for insulin-like peptides in the worm, fly and mammalian nervous systems

Insulin signaling plays a critical role in coupling external changes to animal physiology and behavior. Despite remarkable conservation in the insulin signaling pathway components across species, divergence in the mechanism and function of the signal is evident. Focusing on recent findings from C. elegans, D. melanogaster and mammals, we discuss the role of insulin signaling in regulating adult neuronal function and behavior. In particular, we describe the transcription-dependent and transcription-independent aspects of insulin signaling across these three species. Interestingly, we find evidence of diverse mechanisms underlying complex networks of peptide action in modulating nervous system function.

Adipose tissue insulin receptor knockdown via a new primate-derived hybrid recombinant AAV serotype

Adipose tissue plays an essential role in metabolic homeostasis and holds promise as an alternative depot organ in gene therapy. However, efficient methods of gene transfer into adipose tissue in vivo have yet to be established. Here, we assessed the transduction efficiency to fat depots by a family of novel engineered hybrid capsid serotypes (Rec1~4) recombinant adeno-associated viral (AAV) vectors in comparison with natural serotypes AAV1, AAV8, and AAV9. Rec2 serotype led to widespread transduction in both brown fat and white fat with the highest efficiency among the seven serotypes tested. As a proof-of-efficacy, Rec2 serotype was used to deliver Cre recombinase to adipose tissues of insulin receptor floxed animals. Insulin receptor knockdown led to decreased fat pad mass and morphological and molecular changes in the targeted depot. These novel hybrid AAV vectors can serve as powerful tools to genetically manipulate adipose tissue and provide valuable vehicles to gene therapy targeting adipose tissue.